A cell has an electrolyte and a pair of electrodes separated by the electrolyte. In the case of a fuel cell, a fuel (for example, hydrogen) is supplied to one electrode and an oxidizing agent(for example, oxygen) is supplied to the other electrode. In this way, the chemical energy accompanied by the oxidation of the fuel is converted into electric energy. The electrolyte aims to permeate a hydrogen ion but not a reactant (hydrogen and oxygen). Typically, a fuel cell has a plurality of unit cells, and each unit cell has an electrolyte and a pair of electrodes separated by the electrolyte.
A solid such as a polymer electrolyte membrane and a liquid such as phosphoric acid have been used as the electrolyte of the fuel cell in these days. As the electrolyte of the fuel cell, polymer electrolyte membranes can be suitably employed.
The polymer electrolyte includes, for example, a perfluorosulfonic acid polymer, and the perfluorosulfonic acid polymer typically has such a structure that to a perfluorocarbon backbone (for example, a copolymer of tetra-fluoroethylene and trifluorovinyl), side chains having a sulfonic group (for example, a side chain of a sulfonic group bonded to a perfluoroalkylene group) are bonded. The sulfonic acid group can dissociate a hydrogen ion therein to produce an anion thereby showing proton conductivity. Further, the use of a gel as the electrolyte is proposed.
In addition, as other polymer electrolytes, alkylphosphoric acids of polybenzimidazole are described in Japanese Patent Publication (Kokai) No. Hei 9-110982/1997. It is desirable to produce a polymer electrolyte, which is totally different. On the other hand, polysilamines are reported in the March (1995) issue of Polymer, vol. 44, p. 623.